C++ std::unordered_set membership

C++ std::unordered_set membership

Save as main.cpp and compile with a C++20 compiler, for example g++ -std=c++20 main.cpp -o example. The article states the minimum language version.

#include <unordered_set>
#include <string>
#include <iostream>
int main() {
    std::unordered_set<std::string> seen;
    for (const auto& name : {"Ada", "Lin", "Ada"}) {
        if (seen.insert(name).second) std::cout << name << '\n';
    }
    std::cout << seen.size() << '\n';
}

1. Output: Ada, Lin, then 2. Printing occurs during input traversal, so it does not depend on hash-table iteration order. The syntax illustration uses C++17 structured bindings; the program uses C++11.